This invention relates generally to flat panel display devices and particularly to electron leakage reduction in such devices.
U.S. Pat. No. Re. 30,195 discloses a flat panel display device in which a backplate and a faceplate are spaced in parallel planes. A plurality of vanes extend between the backplate and faceplate to divide the envelope into a plurality of channels and to support the faceplate and backplate against atmospheric pressure after the envelope is evacuated. Arranged in each of the channels is a pair of spaced apart parallel beam guide meshes which extend longitudinally along the channels and transversely across the channels. The beam guide meshes serve as guides along which electron beams are propagated the lengths of the channels.
The inside surface of the faceplate is provided with a phosphor screen which luminesces when struck by electrons. A plurality of extraction electrodes are arranged along the baseplate and are used to eject the electron beams from between the beam guide meshes to direct the electrons toward the phosphor screen. Deflection electrodes are provided on the sides of the support vanes and are electrically energized to cause the electrons to transversely scan across the channels. Accordingly, each of the channels contributes a portion of the total visual display of the device.
U.S. Pat. No. 4,117,368 discloses a flat panel display of the type described above which also includes a plurality of vanes to afford support against atmospheric pressure. Deflection electrodes are provided on both sides of the vanes so that each vane supports one deflection electrode for each of two adjacent channels. In order to avoid charging of the capacitor formed by the deflection electrodes on a single vane, adjacent channels are scanned in opposite directions. Equal scanning voltages therefore are applied to the deflection electrodes on each vane and the detrimental effects of capacitive charging are eliminated.
The inventions described in the above-referenced patents are quite satisfactory for the purpose intended. However, problems arise because of electron leakage from the beam guides. Typically, the first line scanned during the production of a visual display is the line which is furthermost from the cathode and the last line scanned is the line which is nearest to the cathode. Accordingly, the electron beams travel past the last line scanned for a substantial time period during which no line scanning takes place. The opportunity for electron leakage to the screen in the cathode area is thus substantial and a degradation of the visual display frequently results.
The instant invention overcomes the electron leakage problem and thereby greatly enhances the visual display quality.